Search Results (587)

Thermoelectric air conditioning (TEAC) systems are gaining attention as refrigerant-free, solid-state cooling technologies due to their compactness, low noise, and environmental benefits. However, their widespread application is constrained by low energy efficiency and the limited experimental understanding of the coupled influence of electrical and aerodynamic operating parameters. Most existing studies address thermoelectric cooling under isolated conditions or rely on theoretical modeling, leaving a clear gap in the experimental quantification of the interactive effects of applied voltage and air velocity on system performance. To address this gap, the present study experimentally investigates a laboratory-scale TEAC system equipped with four thermoelectric cooler (TEC) modules (model TEC1-12706). The system was tested under controlled conditions by varying the input voltage from 6 to 12 V and the air velocity from 1 to 3 m/s. Key performance indicators, including cooling capacity, power consumption, cold-side temperature, and coefficient of performance (COP), were systematically measured and analyzed. The results show that increasing the applied voltage from 6 to 12 V enhances cooling capacity by approximately 50.4%, while significantly increasing electrical power consumption, leading to a 59% reduction in COP due to intensified Joule heating. Conversely, increasing air velocity improves convective heat transfer, resulting in a COP enhancement of about 24% with relatively stable power input. The findings highlight a clear trade-off between cooling capacity and energy efficiency and identify a practical operating region for balanced TEAC performance. Full article

Wittichenite Cu₃BiS₃ is a promising thermoelectric material with intrinsically low thermal conductivity owing to its complex crystal structure and strong lattice anharmonicity; however, its thermoelectric performance is limited by low carrier concentration and insufficient electrical conductivity. In this study, Cu₃Bi_1−xSn_xS₃ (x = 0.02–0.06) compositions were designed by substituting Sn⁴⁺ for Bi³⁺ sites, and dense single-phase bulk specimens were prepared using mechanical alloying followed by hot pressing. The effects of Sn doping on charge transport and thermoelectric properties were then systematically examined. Structural analysis confirmed that Sn was successfully incorporated into the Cu₃BiS₃ lattice without secondary phase formation, accompanied by anisotropic lattice contraction associated with the difference in ionic radii between Sn⁴⁺ and Bi³⁺. With increasing Sn content, the carrier concentration increased from approximately 10¹⁶ cm⁻³ to the 10¹⁷ cm⁻³ level, whereas the Hall mobility remained nearly unchanged, resulting in a substantial enhancement in electrical conductivity. Although the Seebeck coefficient decreased with increasing carrier concentration, the reduction was moderate, leading to an improved power factor of 0.10 mW·m⁻¹·K⁻² at 673 K. The thermal conductivity remained low, approximately 0.30–0.40 W·m⁻¹·K⁻¹, across the entire composition range, and the electronic contribution was less than 1%, indicating that heat transport was predominantly governed by the lattice contribution. These results demonstrate that Sn doping effectively improves the electrical transport properties while preserving the intrinsically low lattice thermal conductivity of Cu₃BiS₃. Consequently, a maximum ZT of 0.18 was achieved at 673 K, corresponding to a 64% improvement compared with the undoped specimen. Therefore, this study suggests that carrier concentration control via aliovalent doping is an effective strategy for enhancing the thermoelectric performance of wittichenite. Full article

Because antimony trisulfide (Sb₂S₃) is abundant on Earth, non-toxic, and naturally has a low lattice thermal conductivity, it has garnered increasing interest as a possible thermoelectric material. One factor contributing to its anisotropic transport behavior is the orthorhombic structure in which Sb₂S₃ crystallizes, which is made up of one-dimensional (Sb₄S₄)_n ribbons. For thermoelectric energy conversion, its comparatively broad band gap (~1.5–1.7 eV) leads to a high Seebeck coefficient, usually in the 200–600 μV/K range. However, due to its inherently low carrier mobility, pristine Sb₂S₃ exhibits poor electrical conductivity, thereby restricting its power factor. Recent research indicates that composite engineering, nanostructuring, and doping (e.g., with elements such as Ln, As, Se, Ni, Zn, and Fe) can enhance the dimensionless figure of merit (ZT) by increasing carrier concentration while suppressing phonon transport. ZT values in bulk Sb₂S₃ range from 0.1 to 0.2 to approximately 0.5 in optimized nanostructured or doped systems. Higher ZT values (>1) are expected to be possible with advanced band engineering and defect management. According to these results, Sb₂S₃ is a promising mid-temperature thermoelectric material that can be used for waste-heat recovery and possibly integrated into hybrid photovoltaic–thermoelectric systems. Full article

Organic thermoelectric generators (OTEGs) are promising for wearable low-grade heat harvesting, but their device-level output is often limited by interconnect-induced losses. This study investigates flexible OTEGs based on doped single-walled carbon nanotube (SWCNT) thermoelectric clays and optimizes their interconnect structure. P-type and n-type SWCNT clays were prepared by solution processing using TCNQ and TPP as dopants, respectively, and assembled into a five-pair flexible OTEG. The optimized p-type and n-type clays exhibited Seebeck coefficients of 40.81 and −22.42 μV K⁻¹, respectively. The initial OTEG, in which p-type thermoelectric clay was used as the interconnect, delivered a maximum output power of 16.47 nW at ΔT = 21 K. Replacing this thermoelectric-clay interconnect with a compliant Cu-foil/silver-paste interconnect reduced the internal resistance from approximately 372 Ω to 2 Ω, whereas the open-circuit voltage at ΔT = 21 K increased only modestly from 4.95 to 5.08 mV. Under identical controlled temperature-gradient and load-scanning conditions, the optimized OTEG delivered 3.08 μW at ΔT = 21 K, corresponding to a power density of 356.36 nW cm⁻². Mechanical and wrist-worn tests further indicated the flexibility and practical voltage response of the optimized device. These results demonstrate that interconnect optimization is critical for improving SWCNT-clay-based flexible OTEGs. Full article

Increasingly stringent emission regulations in combustion systems drive the demand for robust, cost-effective gas sensors capable of operating under harsh, high-temperature conditions. Thermoelectric ceramic gas sensors represent a promising approach. Their application, however, may be limited owing to a low response. In this work, calcium cobaltite (CCO), a p-type thermoelectric oxide with a Seebeck coefficient higher than most metals used for thermocouples, is investigated as an alternative material to enhance sensor performance. CCO powder was synthesized via the mixed oxide route and deposited as dense ceramic films onto alumina substrates at room temperature using the powder aerosol deposition method (PAD). The thermoelectric properties of the deposited films were characterized up to 850 °C, with the Seebeck coefficient showing only minor dependencies on variations in oxygen and water vapor concentrations. Following these results, planar exothermic gas sensors based on Au/CCO thermocouples utilizing laser-cut polyimide masks for patterning the PAD films were fabricated and compared to reference sensors with screen-printed metallic Au/Pt thermocouples. Laboratory gas measurements with CO and hydrocarbons demonstrated that the Au/CCO-based sensors exhibited an average sensitivity increase by a factor of 8–9, while maintaining high linearity and low cross-sensitivity to variations in oxygen and humidity. Furthermore, the additive response to gas mixtures was confirmed. Initial tests in real flue gas from a wood-burning stove showed an excellent correlation between the sensor signal and relevant flue gas components (measured using precise gas analyzers). The presented results highlight the potential of calcium cobaltite as a thermoelectric material for high-temperature gas sensors based on the exothermic principle and demonstrate the suitability of the PAD method for fabricating fine-structured functional films. Full article

Cu-deficient bornite Cu_5−xFeS₄ (x = 0–0.20) samples were synthesized by mechanical alloying (MA) followed by hot pressing (HP) to investigate the effects of Cu-site non-stoichiometry on structural evolution, charge transport, and thermoelectric performance. X-ray diffraction confirmed single-phase bornite formation after MA, whereas a minor chalcopyrite CuFeS₂ secondary phase appeared in highly Cu-deficient samples after HP, indicating reduced phase stability during thermal consolidation. Rietveld refinement revealed anisotropic lattice distortion and a gradual decrease in unit-cell volume with increasing Cu deficiency. Hall-effect measurements showed that Cu vacancies act as acceptor defects, increasing the hole concentration to the order of 10¹⁸–10¹⁹ cm⁻³ while reducing carrier mobility through enhanced defect scattering. Consequently, the electrical conductivity increased, whereas the Seebeck coefficient decreased with increasing Cu deficiency. The power factor was enhanced, reaching 0.46 mW m⁻¹ K⁻² at 723 K for Cu_4.80FeS₄. The thermal conductivity remained low at 0.48–0.77 W m⁻¹ K⁻¹ owing to dominant lattice contributions and intensified phonon scattering. As a result, Cu_4.80FeS₄ exhibited a 52% higher ZT at 523 K than stoichiometric Cu₅FeS₄, demonstrating that Cu deficiency is an effective strategy for tuning carrier concentration and defect structure in bornite. Full article

This review aims to analyze defect-driven thermoelectric decoupling in pulsed laser deposition (PLD)-grown oxygen-deficient ${WO}_x$ and tungsten Magnéli thin films. While transition metal oxides offer a non-toxic, abundant alternative to conventional thermoelectrics, tungsten oxide stands out due to the profound impact of sub-stoichiometry on its transport properties. We systematically evaluate how ordered oxygen vacancies and crystallographic shear planes transform insulating ${WO}_3$ into sub-stoichiometric phases exhibiting metallic-like conductivity. Specifically, we analyze how the delocalization of W$5d$ electrons around defect-rich regions induces electronic states near the Fermi level, decoupling the Seebeck coefficient from electrical conductivity. Simultaneously, we discuss how these engineered defect networks and shear planes selectively enhance phonon scattering, drastically suppressing lattice thermal conductivity without hindering electronic transport. By establishing PLD as an effective approach for precise oxygen stoichiometry and defect architecture control, this review highlights the high-temperature potential of tungsten Magnéli phases and outlines future pathways to maximize their thermoelectric figure of merit ($ZT$). Full article

Copper selenide (Cu₂Se), as a typical p-type narrow bandgap semiconductor, has garnered significant attention in the fields of thermoelectrics and optoelectronics due to its inherent low thermal conductivity, high Seebeck coefficient, low cost, and environmental friendliness. Compared with bulk materials, Cu₂Se thin films exhibit unique advantages in microdevice integration and flexible applications, holding great potential for applications in flexible thermoelectric generators, solar cells, and photodetectors. This article systematically reviews the research progress of Cu₂Se thin films, focusing on key preparation parameters such as growth temperature, annealing conditions, copper/selenium element ratio, and substrate type, and elucidates their regulation of film microstructure, crystal phase structure, and thermoelectric/optoelectronic properties. It delves into the mechanisms of doping strategies such as carrier concentration regulation, band engineering, and defect modification, clarifying the synergistic optimization effects of different doping elements on conductivity, Seebeck coefficient, and thermal conductivity. The article summarizes the current application status of Cu₂Se thin films, points out existing challenges such as poor process reproducibility and insufficient thermal stability, and anticipates future research directions such as multi-parameter synergistic optimization and heterojunction design, providing a systematic reference for the development and practical application of high-performance Cu₂Se-based functional thin films. Full article

Flexible thermoelectric textiles have emerged as promising materials for wearable energy harvesting and electrothermal applications because they combine mechanical flexibility with the ability to convert low-grade heat into electrical energy. In this study, reduced graphene oxide/zinc oxide/copper oxide (rGO/ZnO/CuO) hybrid nanocomposites were synthesized and deposited onto Cotton–Nylon–Spandex (80:15:05) stretch fabrics using a silicone elastomer-assisted coating process to develop flexible conductive textiles. The influence of nanocomposite loading (2–8 g/100 mL elastomer) on the structural, electrical, thermal, and thermoelectric properties of the coated fabrics was systematically investigated. SEM, EDX, XRD, and Raman analyses confirmed the successful formation and uniform distribution of the rGO/ZnO/CuO hybrid coating on the textile substrate. Increasing the nanocomposite loading progressively reduced the electrical resistance from approximately 42 to 18 MΩ, indicating the formation of an interconnected conductive network, while the Seebeck coefficient increased from 0.049 to 0.056 mV K⁻¹ (49–56 μV K⁻¹). The measured effective thermal conductivity of the coated textile decreased from approximately 12 to 2.68 W m⁻¹ K⁻¹, reflecting changes in the thermal transport behavior of the composite coating. The coated fabrics also exhibited stable electrical performance under repeated bending, stretching (up to 80% strain), and washing, together with improved thermal stability and uniform Joule-heating behavior. These results demonstrate that the rGO/ZnO/CuO hybrid coating provides an effective strategy for developing flexible, mechanically durable, and multifunctional conductive textiles with potential applications in wearable thermoelectric energy harvesting and smart heating systems. Full article

One of the latest and innovative areas of research in energy is the development of thermoelectric generators (TEGs). A novel family of soft, sustainable energy harvesters, hydrogel-based renewable flexible thermoelectric generators use linked ionic, electronic, and redox processes to transform heat gradients into electrical energy. According to recent research, a hydrogel-based TEG has ionic Seebeck coefficients (S) of the order 10–40 mV K⁻¹, which are tens to hundreds of times greater than those of electronic polymers. Thermal conductivities are modest (~0.3–0.6 W/m·K), ionic conductivities typically vary from 10⁻³ to 10⁻¹ S cm⁻¹, and water-rich gels are naturally soft with elastic moduli ~10³–10⁶ Pa and elongations > 100–800%. Recent developments in the concepts, properties, working mechanism, and potential applications of hydrogel-based thermoelectric generators are the focus of this review paper. We investigate the basic transport processes, such as ionic thermodiffusion, thermoelectric ion–electron coupling, and redox-mediated potential production, that allow thermoelectric conversion in hydrogels. This review identifies bottlenecks such as poor output power under minor gradients, summarize performance parameters, and assess methods to improve efficiency. Wearable and implanted power sources, low-grade waste heat collection, and environmental monitoring are examples of promising applications. Lastly, we describe the research avenues that must be pursued in order to expedite the transition of hydrogel-based thermoelectric generators from lab tests to useful, sustainable energy sources. Therefore, the review can provide fundamental knowledge on hydrogel-based TEGs along with their working principles. Full article

PbTe–MgTe based compounds have been demonstrated as promising medium-temperature thermoelectric materials, and significant research efforts have been devoted to enhancing their performance. However, previous studies have primarily focused on low MgTe concentrations (within the solubility limit of ~6 mol%), and a systematic understanding of intrinsic defect behaviors in the PbMgTe solid solution remains lacking. In this work, we perform high-throughput density functional theory calculations to systematically evaluate a comprehensive set of intrinsic defects (including vacancies, anti-sites, and interstitials) in the PbMgTe solid solution modeled by SQS. To the best of our knowledge, this is the first systematic defect study in the PbMgTe system at this composition. Our calculations reveal that vacancies (V_Pb, V_Mg, V_Te) and Mg interstitials (Mg_i) exhibit low formation energies, with acceptor and donor behaviors that effectively facilitate p-type and n-type conductivity, respectively. Notably, these defects induce modifications in the electronic structure that lead to a significant enhancement of the density of states (DOS) near the band edges. Consequently, the Seebeck coefficient is markedly improved compared to that of intrinsic PbMgTe. Our work not only provides valuable insights for defect engineering in PbMgTe-based materials but also establishes a mechanistic link between defect-induced DOS changes and thermopower enhancement, advancing beyond previous studies that focused primarily on formation energies. These findings help bridge the performance gap between n-type and p-type thermoelectric properties. Full article

There has been a rising trend for recovering waste heat, especially after the invention of new types of semiconductors. Among all available utilization options, thermoelectric generation (TEG) systems are promising for recovering waste heat. Thermoelectric devices are environment-friendly, operate silently, and are suitable for low- to high-power applications. This review paper presents a comprehensive study of TEGs, starting with the current problem, state of the art, advantages, disadvantages, generation and related principles, and applications, and covers different arrangements (individual and combined) and working fluids. Furthermore, this article systematically covered various experimental and numerical studies, including optimization, offering insights into heat exchanger configurations, working fluids, and performance parameters. Here, an effort is made to describe the contributions of individual/coupled TEG systems. As a coupled system, the individual TEG system is used with other systems like solar, distillation, solar pond, etc., for cogeneration and enhanced efficiency. The thermal/system parameters of individual/coupled systems are thoroughly discussed, and their impact on efficiency and power generation is illustrated. It was found that the design of the heat exchanger configuration varies from plate type to an efficient liquid-based electricity generation system in these TEG systems. The working fluid inside the fluid loop of a thermoelectric generation system varies from simple fluids to nanofluids. The current state of thermoelectric generation technology is facing challenges in module materials, equipment cost optimization, and commercialization. The progressive TEG generation capabilities have improved with recent advancements in these areas. The power densities are increasing from 0.5 to 1.2 W/cm² in earlier standalone TEGs to 2.5–4.8 W/cm² in recent optimized hybrid configurations, and overall system efficiencies are rising from an average of 5.2% (standalone) to 18.7% in coupled solar-TEG or waste heat recovery systems. The reported maximum ZT values are also improved from ~1.2 to 2.1–2.8 in next-generation materials. Liquid-based heat exchangers in conjunction with nanofluids are the most efficient way to maximize temperature gradient coefficient (0.75–0.92) and minimize parasitic losses. While flexible, ionic, and hybrid next-generation material platforms are still in the early phases of development (TRL 3–5), liquid-based heat exchanger systems improved with nanofluids are closest to commercialization (Technology Readiness Level, TRL 6–8). Therefore, further research in these areas is required to mitigate these challenges. Finally, the recent developments in the thermoelectric generation field and future research direction are briefly discussed. Full article

The nontoxic β-FeSi₂ semiconductor is gaining renewed interest as a thermoelectric material for waste heat recovery. Its earth-abundant elemental composition, consisting of iron (Fe) and silicon (Si), aligns well with the United Nations Sustainable Development Goals. However, the use of the β-FeSi₂ semiconductor is limited by its high electrical resistivity. To improve the thermoelectric properties of the β-FeSi₂ phase, specimens of FeSi₂ were doped with Cu and Al and analyzed. X-ray diffraction and thermal analysis showed that small amounts (up to at least 2%) of Cu and Al dissolved into the FeSi₂ phase. Cu doping reduced the electrical resistivity of FeSi₂ but also lowered the Seebeck coefficient. In contrast, Al doping did not lower the Seebeck coefficient of FeSi₂, while still reducing the electrical resistivity of FeSi₂. Al doping thus improved the power factor of FeSi₂ with 156 μW/mK² and 314 μW/mK² at room temperature for the 1% and 2% Al-doped specimens, respectively. Further thermal conductivity revealed that the Al-doped FeSi₂ specimens showed lower thermal conductivity than the undoped FeSi₂ specimen. Unlike in the case of the electrical resistivity, the 1% Al-doped specimen showed lower thermal conductivity than the 2% Al-doped specimen. The ZT of the 1% Al-doped specimen increased from 0.021 at room temperature to 0.052 at 600 K. This value was slightly higher than that of the Mn-doped β-FeSi₂ but smaller than that of the Co-doped β-FeSi₂. Full article

Thin-film thermocouples (TFTCs) offer conformal sensing junctions with minimal thermal mass, enabling rapid transient response and direct deposition on curved or moving components, which are difficult to achieve using conventional wire thermocouples in applications such as high-speed machining, electric powertrain thermal management, and fuel-cell monitoring. In practical deployment, the effective accuracy of a TFTC can also be affected by the measurement setup used for calibration and testing, particularly lead-wire material transitions, cold-junction compensation, and wiring-related thermoelectric offsets. This study presents a systematic static calibration and performance evaluation of NiCr-based TFTCs under standardised laboratory conditions, with repeated measurements across the 20–260 °C range using both copper leads and matched compensation wires. The thermoelectric output exhibits excellent linearity; temperature reconstruction against a traceable standard reference yields a maximum deviation of approximately 0.27 °C, with root-mean-square and relative errors within tight bounds. Short-term extended-range verification up to 1000 °C confirms detectable thermoelectric signal generation under the present test conditions. A calibration data packet framework containing the calibrated TFTC sample, wiring configuration, calibration coefficients, validity range, and a GUM-compliant uncertainty budget is proposed to support consistent interpretation of calibration results in future digital integration. The study therefore provides a structured calibration workflow and uncertainty-reporting basis for the tested flexible NiCr-based TFTC configurations, supporting further reliability assessment, material-level characterisation, and digital integration. Full article

Wittichenite (Cu₃BiS₃) was synthesized by mechanical alloying (MA) followed by hot pressing (HP), and its phase evolution, thermal stability, charge transport behavior, and thermoelectric performance were systematically examined. X-ray diffraction analysis of the MA powders revealed broadened diffraction peaks, indicating reduced crystallinity and refined crystallite size. After HP consolidation, a well-defined single-phase orthorhombic wittichenite structure was obtained. These results demonstrate that the mechanically induced solid-state synthesis was effectively initiated during MA and subsequently completed through crystallization, defect relaxation, and densification during HP. The MA–HP processed specimens exhibited high relative densities of 94–98% of the theoretical value and a homogeneous microstructure without detectable compositional segregation or grain-boundary enrichment, confirming the formation of a structurally and chemically stable single-phase bulk material. Thermal analysis identified a reversible polymorphic phase transition from P2₁2₁2₁ to Pnma at low temperature, followed by structural relaxation and the onset of partial decomposition at higher temperatures, indicating that Cu₃BiS₃ retains structural integrity below 700 K, which defines the relevant operating window for thermoelectric evaluation. The samples exhibited p-type semiconducting behavior, with electrical conductivity increasing with temperature due to thermally activated hole transport and showing an additional enhancement across the structural transition region. The Seebeck coefficient remained positive over the entire temperature range and decreased gradually with increasing temperature, consistent with semiconductor transport characteristics. The thermal conductivity remained low at 0.30–0.38 W·m⁻¹·K⁻¹, with a negligible electronic contribution, confirming that heat transport is dominated by lattice phonon scattering. As a result of the combined increase in electrical conductivity and intrinsically low thermal conductivity, the dimensionless figure of merit (ZT) increased continuously with temperature and reached 0.17 at 673 K. These results demonstrate that the MA–HP route provides an effective and scalable strategy for producing phase-pure Cu₃BiS₃ with controlled microstructure and reproducible thermoelectric performance. Full article